ZNBG3115Q20 ZETEX [Zetex Semiconductors], ZNBG3115Q20 Datasheet - Page 9

Manufacturer Part Number

ZNBG3115Q20

Description

FET BIAS CONTROLLER WITH POLARISATION SWITCH AND TONE DETECTION

Manufacturer

ZETEX [Zetex Semiconductors]

Datasheet

1.ZNBG3115Q20.pdf (14 pages)

For many LNB applications, tone detection for band switching is required. The ZNBG3115/16 includes all the

circuitry necessary to detect the presence of a 22kHz tone modulated on the supply input to the LNB. The main

elements of the detector are an op-amp, a rectifier/smoother and a comparitor. The op-amp has a pre-set internal

feedback resistor so that just a simple RC network wired to the input gives user defined gain and low frequency

cut filter characteristics. The RC network components also serve two other purposes. The resistor provides

overvoltage protection for the Vpol pin and the capacitor minimises tone interference of the Vpol threshold. The

upper frequency roll-off of the op-amp has been set internally at above 100kHz to allow the amplifier to be used

with other common tone switch frequencies.

The rectifier/smoother/comparitor function is provided by a complex propriety circuit that allows the

ZNBG3115/16 to reliably detect wanted tones whilst ignoring low frequency square wave switch box signals,

DiSEqC™ bursts and supply switching transients common when using DiSEqC-2™ ready set-top boxes. This is

all achieved without the need for any further external components. The threshold of the comparitor is supply

dependent, hence the gain of the preceding op-amp must be adjusted in line with supply voltage. See the table

below for recommended values for 22kHz detection, given for a range of supplies.

Table_1

Note: Optimised for F(tone) = 22kHz.

ISSUE 1 - JUNE 2001

Filter

Components

Rvpol (R2)

Supply Voltage (Vcc)

4.7nF

1.8k

4.7nF

1.5k

10nF

1.3k

10nF

1.1k

ZNBG3115

ZNBG3116

10V

10nF

1.0k